Analysis of fluoroquinolones in dusts from intensive livestock farming and the co-occurrence of fluoroquinolone-resistant Escherichia coli

Fluoroquinolones are important therapeutics in human and veterinary medicine. This study aimed to retrospectively analyse sedimentation dusts from intensive-livestock-farming barns for fluoroquinolones and investigate the association between resistant Escherichia coli and the detected drugs. Sedimentation-dust samples (n = 125) collected (1980-2009) at 14 barns of unknown-treatment status were analysed by HPLC and tandem-mass spectroscopy to detect enrofloxacin, ciprofloxacin, marbofloxacin, and difloxacin. Recent microbiological data were included to investigate the relationship between fluoroquinolone presence and fluoroquinolone-resistant E. coli. Fifty-nine dust samples (47%) from seven barns contained fluoroquinolone residues. Up to three different fluoroquinolones were detected in pig and broiler barns. Fluoroquinolone concentrations ranged from 10-pg/mg to 46-ng/mg dust. Fluoroquinolone-resistant E. coli were isolated from four barns. Of all the dust samples, 22% contained non-susceptible isolates. Non-susceptible isolate presence in the dust was significantly associated (p = 0.0283) with detecting the drugs, while drug detection increased the odds (4-fold) of finding non-susceptible E. coli (odds ratio = 3.9877, 95% CI: 1.2854-12.3712). This retrospective study shows that fluoroquinolone usage leads to dust contamination. We conclude that farmers and animals inhale/swallow fluoroquinolones and fluoroquinolone-resistant bacteria due to drug application. Furthermore, uncontrolled drug emissions via air exhausted from the barns can be assumed.